The dihydrofolate reductase (DHFR) inhibitors are a group of chemical compounds that block the DHFR enzyme, whose main function is to reduce the different forms of folate from the diet to its active form, tetrahydrofolate (THF).
Since the folate in its active form, THF, is used by the cell to produce purines and pyrimidines, which are nitrogenous bases that make up DNA, DHFR has been widely used as a therapeutic target for the treatment of multiple pathological conditions.
Among DHFR inhibitors, methotrexate (MTX) and pemetrexed are the most significant, which are used for, among other applications, in cancer chemotherapy because they are able to prevent the neoplastic cells division.
Microorganisms also need DHFR to grow and multiply, so inhibitors with greater affinity for microbial DHFR are also used in therapy as antibiotic agents; such is the case of trimethoprim (an antibacterial drug) and pyrimethamine (an antiprotozoal drug).
There are treatments for neoplastic diseases such as non-Hodgkin's lymphoma, gestational choriocarcinoma, chorioadenoma, breast cancer, epidermoid cancer, head and neck cancer, T cells cutaneous lymphoma, and lung cancer, in which the prolonged use of DHFR inhibitors in high doses is required. Sustained inhibition of DHFR generates folate deficiencies in its active form, by blocking the body's mechanism to convert folic acid into THF. Due to the high risk of folate deficiency during these types of treatments, medical protocols include folate supplementation in the form of calcium folinate by parenteral route. In this case, the supplementation by parenteral route is feasible because these patients have life-threatening diseases, are hospitalized or go very often to the hospital, and have catheters or venous access devices through which the supplementation can be performed, devices which are usually the same ones used for chemotherapy administration.
On the other hand, there is a group of treatments with DHFR inhibitors that also have a high potential to cause folate deficiencies, for which supplementation with parenteral calcium folinate is not practical because these are outpatients undergoing long-term oral, intramuscular or subcutaneous drug therapy, where venous access is not available. These patients are suffering from rheumatoid arthritis, juvenile rheumatoid arthritis, and psoriasis, which are treated for months, or even years, with low doses of MTX.
In this group of treatments where inhibition of DHFR is also maintained for long periods of time, the conversion of folic acid into THF cannot be carried out properly. That situation, added to the fact that folate supplementation is not included in the treatment protocol, makes folate deficiency in its active form very common in these patients.
The adverse effects caused by DHFR inhibitors are largely due to the same mechanism of action by which they exert their pharmacological effect: decreasing the normal levels of the active form of folate (THF) by inhibiting the DHFR enzyme, which blocks the reduction or activation of folic acid from the diet (FIG. 1).
The adverse effects occurring with prolonged use of low doses of MTX can be classified into three main groups: gastrointestinal adverse effects, mucocutaneous adverse effects and hematological adverse effects.
At gastrointestinal level, folate deficiency may manifest as nausea, anorexia, mild diarrhea, severe ulceration, and bleeding. At mucocutaneous level, the most common manifestation is mouth sores, whereas at hematological level, folate deficiency may decrease the amount of blood cells produced by the bone marrow causing anemia, which in turn manifests as excessive tiredness, paleness, or shortness of breath.
In addition to the adverse effects caused by folate deficiency, at the hepatic level MTX increases transaminases apparently by direct toxicity to the hepatocyte, due to inhibition of synthesis of DNA and RNA in the liver, causing cell deterioration.
For patients treated with MTX, oral folic acid supplementation is not effective because, as mentioned above, folic acid needs the DHFR enzyme to be converted into the active form, THF. When that enzyme is inhibited, the activation step of folic acid by conversion into THF cannot occur, and folate deposits cannot be restored.
Moreover, supplementation of folate alone is not enough to avoid comprehensively the occurrence of adverse effects due to the treatment with MTX because, as mentioned before, the toxic effect on the liver is caused by a direct effect of MTX on the hepatocyte; so, the restoration of deposits of folate by intravenous administration should be accompanied with a protective action on the liver that prevents elevation of transaminases.
Therefore, there is the need, in the state of the art, of means to restore the decreased folate deposits due to MTX treatment with an oral pharmaceutical composition to allow the administration of a form of folate that does not require the mediation of DHFR to become active, which also protects the liver against the action of MTX.
In the state of the art there are some documents including compositions containing folate, such as the International Publication WO 2007/013987, which discloses a composition for improving the methylation process and reducing the likelihood that the individual will develop clinical conditions caused by deficiency in the methylation process. This composition comprises vitamin B6, folic acid, vitamin B12, betaine and silymarin.
The U.S. Pat. No. 7,947,662 discloses a composition for the treatment of diseases such as psoriasis and arthritic and inflammatory conditions, which comprises folic acid, vitamins, botanical extracts and some amino acids. This composition is chemically stable and has high water solubility of folates and/or reduced folates.
The American Publication US 2014/0073598 discloses compositions to be used in patients lacking the ability to convert folic acid into its metabolically active forms, and in the treatment of depression. This composition comprises folate, vitamin B12 and vitamin B6.
The U.S. Pat. No. 8,642,581 discloses the method to increase the levels of S-adenosylmethionine in the human body without the administration of S-adenosylmethionine, by the direct administration of L-methionine, methylcobalamin, 5-methyltetrahydrofolate, betaine, and malic acid with at least one compound selected from the group consisting of folic acid, vitamin B12, magnesium, calcium, and other cofactors.
However, the state of the art does not provide compositions easy to administer that allow the administration of the active form of folate, while protecting the liver against the adverse effects associated with a prolonged treatment with DHFR inhibitors, such as MTX.